US3692645A - Electrolytic process - Google Patents

Electrolytic process Download PDF

Info

Publication number
US3692645A
US3692645A US82153A US3692645DA US3692645A US 3692645 A US3692645 A US 3692645A US 82153 A US82153 A US 82153A US 3692645D A US3692645D A US 3692645DA US 3692645 A US3692645 A US 3692645A
Authority
US
United States
Prior art keywords
oxygen
anode
melt
electrolysis
carbon
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US82153A
Inventor
Borut Marincek
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alcan Holdings Switzerland AG
Original Assignee
Alusuisse Holdings AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alusuisse Holdings AG filed Critical Alusuisse Holdings AG
Application granted granted Critical
Publication of US3692645A publication Critical patent/US3692645A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25CPROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium

Definitions

  • the electrolysis of molten materials is carried out today with carbon anodes.
  • the oxygen ions formed during the electrolysis react with the carbon of the anode at the process temperatures of 900 to 1000 C. and form carbon dioxide, which is partly reduced to carbon monoxide by the aluminium itself.
  • the carbon anode is consumed and, in fact, if only carbon dioxide were to be formed, 334 kg. of carbon per ton of aluminium produced would be consumed. In practice, about 400 to 450 kg.
  • I use an anode of any suitable conducting material, and I separate this anode from the melt being electrolysed by a layer of material which is oxygen-ions-conducting but non-permeable to and resistant to the melt at the temperature of the electrolysis, so that the oxygen ions diffuse through the layer and are then discharged at the anode with the formation of oxygen gas.
  • the anode itself preferably consists of an electronice conducting material which does not react with oxygen or at least does not form with oxygen any compound impairing the conduction of electrons. Suitable materials include heat-resistant alloys, platinum or other noble metals, electron-conducting oxides, such as for example, wiistite, certain materials with semi-conductor properties, and metals with a passivated surface.
  • the thickness of the oxygen-ion-conducting layer may be very small so that the voltage drop across it is also small; this reduces losses of energy during the electrolysis.
  • stabilised forms of zirconium oxide are very suitable as the material which separates the anode from the melt.
  • stabilised I mean zirconium oxide in which is incorporated proportions of other oxides such as calcium oxide, magnesium oxide and yttrium oxide, which serve firstly to stabilise the cubic (fluorite) lattice of the zirconium oxide, and secondly to confer on it the necessary oxygen-ion conductivity.
  • a stabilised zirconium oxide can have a resistance as low as 10 ohms-cm. at 1000 C.
  • refractory oxides which have fluorite lattices can be used, such as for example, rare earth oxide-uranium oxide compositions, thorium oxide-uranium oxide compositions and cerium oxide suitably stabilised with calcium oxide or magnesium oxide. Substances which reduce the solubility of the oxygen-ion-conducting material may be added to the fused melt.
  • the invention will be described hereinafter with specific reference to the electrolysis of alumina for the production of aluminium.
  • the oxygen ions which are formed in accordance with the equation dilfuse through the oxygen-conductive layer and are discharged at the anode in accordance with the equation i.e. the oxygen ions combine to form oxygen gas and electrons are released in the process. These electrons are conducted away by the anode.
  • Other oxides such as for in stance, MgO, Na O, CaO, Fe O can also be electrolysed by the process according to the invention and similar equations can be formulated.
  • cells according to the invention atford the following advantages, inter alia, in comparison with the present state of the art. I
  • Cells according to the invention can readily be adapted for automation of operation with for example, continuous addition of alumina to the fused melt and maintenance of constant interelectrode gap or cell voltage.
  • Cells according to the invention may be constructed in two Ways.
  • the anode is coated with or is in contact with the layer of oxygen-ion-conducting material over at least that part of its surface which is immersed in the melt; the anode must then be in such a physical state that oxygen gas can pass through it.
  • the anode may be solid, in which case it must be porous, perforated or reticulated.
  • the layer of oxygen-ion-conductin'g material may be applied directly to it by pressing or casting with subsequent drying and sintering or by plasma spraying.
  • a body of the material may be preformed quite separately and put in contact with the anode, if the latter is, for example, a metal network.
  • a porous layer of platinum black may be applied to a preformed body of the material, and electrically connected to one terminal of the current supply. This last proposal is found to be very satisfactory, as platinum black is particularly suitable for the discharge of oxygen ions and the formation and removal of oxygen gas.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)

Abstract

PROCESS FOR THE ELECTROLYSIS OF MOLTEN OXIDES, ESPECIALLY OF ALUMINA, IN WHICH A GAS PERMEABLE ANODE IS SEPARATED FROM THE MELT BEING ELECTROLYZED BY A LAYER IN CONTACT WITH THE ANODE AND THE MELT, OF AN OXYGEN-ION-CONDUCTING MATERIAL, FOR EXAMPLE ZIRCONIUM OXIDE STABILIZED WITH CALCIUM OXIDE OR OTHER OXIDES, WHICH IS RESISTANT TO THE MELT AT THE TEMPERATURE OF THE ELECTROLYSIS.

Description

United States Patent US. Cl. 204-67 1 Claim ABSTRACT OF THE DISCLOSURE Process for the electrolysis of molten oxides, especially of alumina, in which a gas permeable anode is separated from the melt being electrolyzed by a layer, in contact with the anode and the melt, of an oxygen-ion-conducting material, for example zirconium oxide stabilized with calcium oxide or other oxides, which is resistant to the melt at the temperature of the electrolysis.
CROSS REFERENCE TO RELATED APPLICATION This application is a division of my copending application Ser. No. 638,249, filed May 15, 1967, now U.S. Pat. 3,562,135, patented Feb. 9, 1971.
BACKGROUND OF THE INVENTION The electrolysis of molten materials, for example of alumina, is carried out today with carbon anodes. In the case of alumina, the oxygen ions formed during the electrolysis react with the carbon of the anode at the process temperatures of 900 to 1000 C. and form carbon dioxide, which is partly reduced to carbon monoxide by the aluminium itself. Owing to the oxidation of the anode by the nascent oxygen, the carbon anode is consumed and, in fact, if only carbon dioxide were to be formed, 334 kg. of carbon per ton of aluminium produced would be consumed. In practice, about 400 to 450 kg. of anode carbon are consumed per ton of aluminium, which corresponds to about 8 to 10% of the cost of crude aluminium. It has only recently been possible to reduce the consumption of anode carbon even to this figure, and with the present method of working using carbon anodes, reduction of the consumption of anode carbon below the theoreticall smallest amount, that is 334 kg. of carbon per ton of aluminium, is not possible.
It has now been found that it is possible to carry out the melt electrolysis of oxides without using carbon anodes, but using electrodes which are oxygen-resistant Without necessarily being resistant to attack by the melt being electrolyzed, so that the oxygen can be obtained as a valuable by-product of the process. About 600 mm. of pure gaseous oxygen are formed per ton of aluminium; the value of the oxygen is about 3% of the cost of the crude aluminium. The oxygen which can be recovered in carrying out the process according to the invention into effect can be used for various oxidising processes, such as for example, steel production (by the oxygen blow method), the gasification of fuels (for producing synthetic gas) and the preparation of reducing gases for iron reduction.
According to the invention I use an anode of any suitable conducting material, and I separate this anode from the melt being electrolysed by a layer of material which is oxygen-ions-conducting but non-permeable to and resistant to the melt at the temperature of the electrolysis, so that the oxygen ions diffuse through the layer and are then discharged at the anode with the formation of oxygen gas. The anode itself preferably consists of an electronice conducting material which does not react with oxygen or at least does not form with oxygen any compound impairing the conduction of electrons. Suitable materials include heat-resistant alloys, platinum or other noble metals, electron-conducting oxides, such as for example, wiistite, certain materials with semi-conductor properties, and metals with a passivated surface. The thickness of the oxygen-ion-conducting layer may be very small so that the voltage drop across it is also small; this reduces losses of energy during the electrolysis.
SUMMARY I have found that know stabilised forms of zirconium oxide are very suitable as the material which separates the anode from the melt. By stabilised I mean zirconium oxide in which is incorporated proportions of other oxides such as calcium oxide, magnesium oxide and yttrium oxide, which serve firstly to stabilise the cubic (fluorite) lattice of the zirconium oxide, and secondly to confer on it the necessary oxygen-ion conductivity. By suitable choice of oxides and their proportions, a stabilised zirconium oxide can have a resistance as low as 10 ohms-cm. at 1000 C. Other refractory oxides which have fluorite lattices can be used, such as for example, rare earth oxide-uranium oxide compositions, thorium oxide-uranium oxide compositions and cerium oxide suitably stabilised with calcium oxide or magnesium oxide. Substances which reduce the solubility of the oxygen-ion-conducting material may be added to the fused melt.
The invention will be described hereinafter with specific reference to the electrolysis of alumina for the production of aluminium. In such an electrolysis, the oxygen ions which are formed in accordance with the equation dilfuse through the oxygen-conductive layer and are discharged at the anode in accordance with the equation i.e. the oxygen ions combine to form oxygen gas and electrons are released in the process. These electrons are conducted away by the anode. Other oxides such as for in stance, MgO, Na O, CaO, Fe O can also be electrolysed by the process according to the invention and similar equations can be formulated. In the electrolysis of alumina for example, cells according to the invention atford the following advantages, inter alia, in comparison with the present state of the art. I
(1) There is no consumption, or only a very low rate of consumption, of anode material with the result that the rate of production of anode material can be substantially reduced.
-(2) The formation of carbon scum in the bath results in a loss of operating efficiency, and this formation will not occur if the anodes are of material other than carbon.
(3) There is improvement of the quality of the aluminium metal produced, since no impurities, such as iron, silicon or vanadium are introduced from the anodes material.
(4) There is less down-time of the cell, since the anodes do not have to be replaced.
(5) There is a reduction of the consumption of fiuxing materials, since the cell can be sealed off more satisfactorily and this also gives an improvement in the shop atmosphere.
(6) Pure oxygen can be produced and collected as a byproduct.
(7) There is no re-oxidation of the liquid aluminium by carbon dioxide and thus, there is increased output from the cell and a reduction in the energy required to produce a given weight of aluminium.
Cells according to the invention can readily be adapted for automation of operation with for example, continuous addition of alumina to the fused melt and maintenance of constant interelectrode gap or cell voltage.
Cells according to the invention may be constructed in two Ways. In the first of these, the anode is coated with or is in contact with the layer of oxygen-ion-conducting material over at least that part of its surface which is immersed in the melt; the anode must then be in such a physical state that oxygen gas can pass through it.
The anode may be solid, in which case it must be porous, perforated or reticulated.
If the anode is solid, the layer of oxygen-ion-conductin'g material may be applied directly to it by pressing or casting with subsequent drying and sintering or by plasma spraying. Alternatively a body of the material may be preformed quite separately and put in contact with the anode, if the latter is, for example, a metal network. As a further possibility, a porous layer of platinum black may be applied to a preformed body of the material, and electrically connected to one terminal of the current supply. This last proposal is found to be very satisfactory, as platinum black is particularly suitable for the discharge of oxygen ions and the formation and removal of oxygen gas.
What is claimed is:
1. The method of reducing molten oxide by electrolysis in an electrolytic cell which comprises passing a direct electric current between a cathode in contact with the melt and a gas permeable anode resistant to the formation with oxygen of any compound impairing the conduction of electrons, said anode being separated from the molten oxide of the melt by a layer of solid material in contact with the anode and immersed in and in contact with the melt and which is oxygen-ion-conducting but non-permeable to and resistant to the material of the melt at the temperature of the electrolysis, and said current as it passes through the cell causing diffusion of oxygen-ions through said layer of material with the formation of oxygen gas References Cited UNITED STATES PATENTS 6/1971 Stewart 20464 X 9/1968 Tasiri et a1. 204--11 JOHN H. MACK, Primary Examiner N. A. KAPLAN, Assistant Examiner U.S. Cl. X.R. 20464 R,
US82153A 1967-05-15 1970-10-19 Electrolytic process Expired - Lifetime US3692645A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US63824967A 1967-05-15 1967-05-15
US8215370A 1970-10-19 1970-10-19

Publications (1)

Publication Number Publication Date
US3692645A true US3692645A (en) 1972-09-19

Family

ID=26767123

Family Applications (1)

Application Number Title Priority Date Filing Date
US82153A Expired - Lifetime US3692645A (en) 1967-05-15 1970-10-19 Electrolytic process

Country Status (1)

Country Link
US (1) US3692645A (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4582584A (en) * 1985-03-07 1986-04-15 Atlantic Richfield Company Metal electrolysis using a semiconductive metal oxide composite anode
US4614569A (en) * 1983-01-14 1986-09-30 Eltech Systems Corporation Molten salt electrowinning method, anode and manufacture thereof
US5942097A (en) * 1997-12-05 1999-08-24 The Ohio State University Method and apparatus featuring a non-consumable anode for the electrowinning of aluminum
US6187168B1 (en) 1998-10-06 2001-02-13 Aluminum Company Of America Electrolysis in a cell having a solid oxide ion conductor
US6299742B1 (en) 1997-01-06 2001-10-09 Trustees Of Boston University Apparatus for metal extraction

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4614569A (en) * 1983-01-14 1986-09-30 Eltech Systems Corporation Molten salt electrowinning method, anode and manufacture thereof
US4582584A (en) * 1985-03-07 1986-04-15 Atlantic Richfield Company Metal electrolysis using a semiconductive metal oxide composite anode
US6299742B1 (en) 1997-01-06 2001-10-09 Trustees Of Boston University Apparatus for metal extraction
US5942097A (en) * 1997-12-05 1999-08-24 The Ohio State University Method and apparatus featuring a non-consumable anode for the electrowinning of aluminum
US6187168B1 (en) 1998-10-06 2001-02-13 Aluminum Company Of America Electrolysis in a cell having a solid oxide ion conductor

Similar Documents

Publication Publication Date Title
US3562135A (en) Electrolytic cell
Yan et al. Production of niobium powder by direct electrochemical reduction of solid Nb 2 O 5 in a eutectic CaCl 2-NaCl melt
JP5562962B2 (en) Oxygen generating metal anode operating at high current density for aluminum reduction cells
US3930967A (en) Process for the electrolysis of a molten charge using inconsumable bi-polar electrodes
EA007046B1 (en) Reduction of metal oxides in an electrolytic cell
EA013139B1 (en) Electrode
GB833767A (en) Continuous electrolytic production of titanium
BR0115346B1 (en) Process for the Production of an Intermetallic Compound (M1Z)
ES430848A1 (en) Process for the electrolysis of a molten charge using inconsumable anodes
US2302604A (en) Fused bath electrolytic production of ferrochromium
CN101280438A (en) Method for directly preparing ferrochromium alloy with chromite powder
US3692645A (en) Electrolytic process
Kim et al. Stability of iridium anode in molten oxide electrolysis for ironmaking: influence of slag basicity
US4504369A (en) Method to improve the performance of non-consumable anodes in the electrolysis of metal
Namboothiri et al. Aluminium production options with a focus on the use of a hydrogen anode: a review
Sleppy et al. Bench scale electrolysis of alumina in sodium fluoride-Aluminum fluoride melts below 900 C
JP4198439B2 (en) Consumable carbon anode for smelting titanium metal
CN114182301A (en) Method for preparing metal beryllium by electrolyzing beryllium oxide through fluoride molten salt
EA014138B1 (en) Electrochemical reduction of metal oxides
Xuyang et al. Effect of electrical conductivity and porosity of cathode on electro-deoxidation process of ilmenite concentrate
US2952591A (en) Electrolytic preparation of calcium carbide
US771646A (en) Process of obtaining metals.
US3503857A (en) Method for producing magnesium ferrosilicon
Güden et al. Electrolysis of MgCl2 with a top inserted anode and an Mg-Pb cathode
US3560353A (en) Electrolysis cell current efficiency with oxygen-containing gases